phthalocyanine nanocomposites for the degradation of selected industrial dyes

Accepted Manuscript Enhanced visible light photocatalysis using TiO2/Phthalocyanine nanocomposites for the degradation of selected industrial dyes K.P. Priyanka, S. Sankararaman, K.M. Balakrishna, Thomas Varghese PII:

S0925-8388(17)31925-4

DOI:

10.1016/j.jallcom.2017.05.308

Reference:

JALCOM 42039

To appear in:

Journal of Alloys and Compounds

Received Date: 1 April 2017 Revised Date:

7 May 2017

Accepted Date: 28 May 2017

Please cite this article as: K.P. Priyanka, S. Sankararaman, K.M. Balakrishna, T. Varghese, Enhanced visible light photocatalysis using TiO2/Phthalocyanine nanocomposites for the degradation of selected industrial dyes, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.05.308. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Enhanced Visible Light Photocatalysis using TiO2/Phthalocyanine Nanocomposites for the Degradation of Selected Industrial Dyes Priyanka K. P.1, Sankararaman S.2, Balakrishna K. M.1 and Thomas Varghese3* 1

Dept. of Physics, Mangalore University, Mangalagangotri-574 199, Karnataka, India

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2

Dept. of Optoelectronics, Uniersity of Kerala, Thiruvanathapuram-695581, Kerala, India

3

Nanoscience Research Centre (NSRC), Dept. of Physics, Nirmala College, Muvattupuzha-686 661,

Kerala, India

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*Corresponding author e-mail: [email protected]

Abstract

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Solvent-evaporation method has been successfully employed for the synthesis of titanium dioxide/metal phthalocyanine (TiO2/M-Pc (M=Co, Fe)) nanocomposites. Systematic investigations of thermal, structural and optical properties of the synthesized composites were carried out. Fourier transform infra-red and Raman spectroscopic studies confirmed the successful formation of TiO2/M-Pc nanocomposites. Optical absorption studies for the samples

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demonstrate the optical band gap tuning from UV to visible regime. The photoluminescence studies of the synthesized nanocomposites found blue – green emission for potential use in near

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UV light excited light emitting diodes and other display devices. The photocatalytic degradation studies of certain industrial dyes using the synthesized nanocomposites found that almost 100%

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of organic pollutants are decomposed within 90 minutes of visible light irradiation. In brief, the present study confirms the potential use of TiO2/MPc nanocomposite in the field of industrial applications to eliminate the organic pollutants from waste water. Keywords: TiO2/phthalocyanine composite; UV-Vis spectrum; photocatalysis 1 Introduction The presence of organic pollutants in the environment and ecosystem causes much trouble on public health worldwide. The toxicity and persistence of these organic pollutants

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ejected from food processing, agricultural and textile industries adversely affect the marine and aquatic life. In order to safeguard ourselves, it is essential to find methods to detoxify these organic pollutants. Among several proposed processes for waste water treatment, the most

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important method is photocatalytic oxidation. In this scenario, the combination of inorganicorganic nanocomposites has the potential in many areas due to the binding of different physical and chemical properties of the two types of materials together [1]. The organic materials show

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high thermal and chemical properties, nontoxicity, semiconductivity, and interesting optical properties [2]. But, inorganic metal oxide nanoparticles provide the potential for high carrier

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mobilities, band-gap tunability, good thermal and mechanical stability, and a range of magnetic and dielectric properties [1]. The unique properties possessed by phthalocyanines (among macrocyclic organic compounds) and TiO2 (among metal oxide semiconductors) offer a potential combination of organic–inorganic nanocomposite material.

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A number of literatures were reported on the study of TiO2/CoPc or TiO2/FePc nanocomposites. Ishida et al. investigated the adsorption of cobalt-substituted phthalocyanines on rutile (110) surface and observed that the adsorption properties were strongly dependent on

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the deposition process [3]. A series of works have been reported on metal phthlaocyanines/TiO2 nanocomposites as a photocatalyst by certain researchers [4-7]. Photocatalytic reduction of

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carbon dioxide using titania supported CoPc catalysts was reported [8, 9]. Iron phthalocyanine modified titanium dioxide showed better activity for the degradation of organic pollutants as compared to non-modified TiO2 as observed by Ranjith et al. [10]. Photovoltaic response of FePc/TiO2 thin films was studied by Sharma and his team [11]. It is noteworthy that detailed characteristic studies regarding thermal, structural, optical and electrical properties of TiO2/M-Pc (M=Co, Fe) along with its photocatalytic activity under

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visible light are sparse. In the present study, the focus is towards the synthesis and characterization

of

titanium

dioxide/metal

phthalocyanine

(TiO2/M-Pc;

M=Co,

Fe)

nanocomposites. Particular emphasis has been given on the photocatalytic degradation of certain

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industrial dyes (methylene blue and rhodamine blue) under visible light using the synthesized

promising use in the field of water purification. 2 Materials and methods 2.1 Synthesis of TiO2/M-Pc Nanocomposite

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nanocomposite. The photocatalytic efficiency possessed by these nanocomposites assures their

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TiO2/M-Pc nanocomposite samples were prepared by following simple solvent evaporation method. Sol-gel prepared TiO2 nanoparticles, cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) (Sigma-Aldrich Chemicals, Mumbai, India), dimethyl formamide, dimethyl sulphoxide, and ethanol (Merck, Whitehouse Station, NJ) were used for the synthesis of

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the nanocomposite.

The scheme for the synthesis of TiO2/M-Pc is shown in Fig.1. The composites were prepared by coating TiO2 nanoparticles with cobalt/iron phthalocyanine (1wt%; wt% is the mass

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ratio of M-Pc to TiO2), dissolved in a solvent mixture containing 50% dimethyl sulphoxide, 30% dimethyl formamide and 20% ethanol. The mixture was stirred at 60oC using magnetic stirrer.

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Synthesis of TiO2 nanoparticles using sol-gel method has been described elsewhere [12]. The required amount of TiO2 nanoparticles calcined at 400oC was gradually added to the mixture solution under stirring and heating, resulting in a suspension with homogeneous appearance. After complete solvent evaporation, the obtained material was washed several times with distilled water under vigorous stirring to remove residues and remaining organic solvent. The composite was further dried at 100oC in a hot air oven for 15-20 h. The obtained powder was

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crushed well using mortar and pestle. The final product was fine powders with bluish appearance for TiO2/CoPc sample, and a mix of pale green and yellow for TiO2/FePc sample. The sol-gel

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nanocomposite samples are denoted as S0, S1 and S2, respectively.

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prepared TiO2 nanoparticles calcined at 400oC, TiO2/CoPc nanocomposite and TiO2/FePc

Fig. 1 Scheme of preparation of TiO2/M-Pc nanocomposite

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The synthesized samples were characterized by thermogravimetric and differential

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thermal analysis (TGA/DTA) (Perkin Elmer STA 6000, at a heating rate of 10° C/min), X-ray diffraction (XRD) (Bruker D8 advance X-ray diffractometer with Cukα1 = 1.5406 Å radiation), Fourier transform infra-red spectroscopy (FTIR) (IR Prestige 21 Shimadzu FTIR with SPECCAC ATR model spectrometer) and Raman spectroscopy (Raman spectrometer, Bruker RFS-27, using Nd-YAG laser of wavelength λ=1064 nm). The morphology of the samples was analyzed using scanning electron microscopy (SEM) using Jeol Model JSM-6390LV Scanning electron microscope, operating at 20 kV and transmission electron microscopy (TEM) using Jeol

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JEM 2100 accelerated by 200kV. Chemical sample analyses were performed by energydispersive X-ray spectroscopy (EDX) using Jeol Model JED-2300 equipment with an accelerating voltage of 30 kV.

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The optical properties of the pure and composite samples were studied by UV-Vis analysis (Shimadzu 2600 UV-visible spectrophotometer) and Photoluminescence (PL) spectroscopy (Fluoromax-3 spectrophotometer). Absorbance of powder samples can be obtained

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from the reflectance measurements by performing Kubelka-Munk transformation. The absorption coefficient α is related to the photon energy hν by the relation, α= α0 (hν-Eg)1/2, where

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Eg is the optical band gap.

2.2 Photocatalytic activity testing using the synthesized nanocomposites The photocatalytic activity of the synthesized TiO2/M-Pc (M=Co, Fe) nanocomposites was investigated by the degradation of methylene blue (MB) and rhodamine blue (RB)

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(industrial organic dyes) under visible light irradiation. 100 mg of the catalyst sample was transferred into 100 ml of 4×10-5 M dye solution. The mixture of dye and photocatalyst was kept in the dark for 30 min under stirring conditions in order to attain adsorption-desorption

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equilibrium between the photocatalyst and dye. The reaction mixture was then exposed to sunlight on a sunny day when sunlight with bright and constant intensity was available. The

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intensity of the sunlight was measured (1.501 Wm-2) using YSI 9500 photometer. At specific time intervals (15 min), the reaction solution was withdrawn and was centrifuged to remove the catalyst sample. The degradation of organic dyes was evaluated by measuring optical absorption of reaction mixture using UV-Vis absorption analysis. Another reaction was carried out using all the samples under the same reaction conditions but by keeping in dark. The percentage of degradation is given as (C/C0) x100, where C was the main absorption peak intensity of dye

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solution at each irradiated time interval and C0 was the absorption intensity of starting concentration of dye solution. 3 Result and discussion

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3.1 Thermal analysis

Fig. 2 (a) and (b) represents the thermogravimetric analysis curves for the TiO2/M-Pc nanocomposites. TGA curves for samples S1 and S2 show a small weight loss from room

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temperature to 700°C. From room temperature to 400°C, weight loss is due to residual water evaporation for the two composites. However, from 400 to 600°C, the weight loss is due to

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partial decomposition of macrocyclic structure, where low weight atoms (H and part of N) are lost from composite structure [13]. The total weight loss is around 7% for S1 and around 9% for S2, which confirm the thermal stability of the nanocomposites. The DTG curves of samples S1and S2 show three endothermic peaks below 300°C, and these weight losses are due to the

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combustion of organic residues or fragmentation of one unit of peripheral environment of the phthalocyanine molecule [14]. The endothermic peaks are positioned around 67.07, 168.67 and

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282.900C for sample S1 and 71.77, 175.78 and 268.350C for S2.

Fig. 2 (a) TGA/DTA graph of sample S1

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3.2 Structural analysis 3.2.1 Powder XRD analysis

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Fig. 2 (b) TGA/DTA graph of sample S2

Fig. 3 represents the XRD patterns of the synthesized nanocomposites and pure TiO2 samples. The XRD pattern of the sample S0 reveals the presence of TiO2 anatase phase with

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tetragonal structure, which is in agreement with JCPDS file no. 73–1764 for TiO2.

Fig. 3 XRD patterns of samples S0, S1 and S2

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The crystalline nature of the synthesized nanocomposite is evident from the sharp diffraction peaks in the XRD patterns of S1 and S2. For S1, the composite structure is composed of anatase - rutile mixed phase. Using Spurr equation [15], the weight percentage of rutile in S1

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is estimated to be 64.6%. This indicates the formation of rutile phase without calcination treatment in TiO2 nanocomposites, which is reported for the first time. Zhao et al. have found the formation of rutile phase after a heat treatment at high temperature, and they observed that the

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dispersion of CoPc in TiO2 lattice caused the decrease of phase transformation temperature from

for rutile phase to grow than anatase [9].

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anatase to rutile. This may be the disfigurement of CoPc into TiO2, which was more profitable

The peaks of rutile TiO2 in S1 are indexed to a tetragonal structure (JCPDS file no.78– 1510 for TiO2). There is a single peak of lower intensity at 43.95o, which corresponds to α-CoPc phase unit cells (ICCD card No. 02-0312). However, there are no additional characteristic peaks

concentration of CoPc [9].

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of phthalocyanine in the diffraction pattern of S1, which was most likely due to lower

XRD pattern of S2 shows that all the peaks represent anatase phase of TiO2, satisfying

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JCPDS file no. 73–1764. A low intensity rutile plane (110) is also visible in the XRD pattern. There is no peak of phthalocyanine seen in the diffractogram of S2, which might be due to the

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complete dispersion of FePc into TiO2 [9]. In all the XRD patterns, a low intensity brookite phase of (121) plane is observed.

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Peak position (2θ)

FWHM (rad)

d value (Å)

Average crystallite size (D) (nm)

Dislocation density (nm-2)

S0

25.6

0.0225

3.478

6

0.02778

S1

25.31

0.0167

3.515

8.38

0.01424

S2

25.28

0.0179

3.519

7.82

Lattice constants

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Sample

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Table 1. Structural parameters of S0, S1and S2 from XRD analysis

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0.01635

a=b= 3.773; c = 9.492

a=b= 3.793; c = 9.357 a=b= 3.792; c = 9.442

Structural parameters of samples calculated from XRD patterns is given in the table 1. It is clear from the table that full width at half maximum (FWHM) of the diffraction peaks are smaller for the composites (S1 and S2) and their peak positions are shifted towards lower angle,

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which implies the formation of larger crystallites. Average crystallite sizes estimated by using Scherrer’s equation [16] are 6, 8.38 and 7.82 nm for samples S0, S1 and S2, respectively. A slight increment in crystallite size and interplanar spacing (d values given in the table 1) is also

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observed for nanocomposites, attributed to the expansion of unit cell with the addition of

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phthalocyanines in TiO2. Dislocation density (K=1/D2, where D is the crystallite size) and the lattice constants calculated for nanocomposites also show considerable variations from that of pure TiO2 nanoparticles, which may be due to the formation of defect centres during composite formation.

3.2.2 SEM and EDX Fig. 4 shows SEM images of S0, S1 and S2 samples. For nanocomposites, the micrographs show more clusters of spherical particles indicating particle growth. In S1, particles

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are aggregated together leaving no space in between them, while S2 shows the formation of homogeneous spherical nanoparticles. Comparing with pure TiO2 nanoparticles, the morphology

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of the S2 is almost remains the same; the change becomes visible in the form of particle growth.

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Fig. 4 SEM images of samples S0, S1 and S2

Using energy dispersive X-ray analysis, the chemical composition of the nanocomposites was determined. Fig. 5 (a) and (b) represent the signals corresponding to titanium, oxygen, carbon, nitrogen, cobalt and iron. Absence of other element peaks in the spectrum shows the

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purity of the prepared nanocomposites.

Fig. 5 (a) Chemical composition of S1 nanocomposite

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Fig. 5 (b) Chemical composition of S2 nanocomposite

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3.2.3 TEM

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Fig. 6 TEM images of samples S0, S1 and S2

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Fig.6 shows TEM bright field images of pure and composite samples. The composite particles are dispersed together as observed from the images of S1 and S2. The average particle sizes obtained from TEM images are 6.5, 8.5 and 7 nm for S0, S1 and S2 respectively. The particle sizes obtained from TEM images are in agreement with the XRD results. 3.2.4 FTIR Fig. 7 represents the FTIR spectra of the pure TiO2 and M-Pc nanocomposites. Comparing with pure TiO2, FTIR spectra of the composite samples shows some major peaks due

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to the presence of cobalt/iron phthalocyanine. Table 2 gives a comparison between observed

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modes in S0, S1 and S2.

Fig. 7 FTIR spectra of S0, S1 and S2

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From table 2, sample S0 shows vibrational modes in the range of 520-408 and 14581416, which corresponds to Ti-O and Ti-O-Ti modes of vibration in TiO2 nanoparticles [17-20]. The Ti-O band is found to be red shifted to 542 and 557 cm-1 for nanocomposite samples S1 and

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S2 respectively, which might be due to the incorporation of TiO2 with phthalocyanines. In the spectrum of S1, bands at 628 (C–C out-of-plane ring deformation), 726 (C–H out-of-plane

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deformation), 964 (metal-ligand vibration), 1031 (C–H in-plane deformation), 1328 (C–C stretching) and 1520 (C–N stretching) attribute the presence of CoPc in the composite [9, 17]. Out of these, band at 726 cm-1 represents the characteristic band of α-phase of CoPc [21]. Thus, the successful formation of TiO2/CoPc nanocomposite is confirmed from FTIR spectrum.

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Table 2. Comparison of IR active modes of S0, S1 and S2 Literature values FePc cm-1 [18] --

--967 1047 1394 --

634 721 911 1069 1329 --

-727 -1143 1382 --

1530 1650 36183738

1521 ---

--3328

S1 cm-1

S2 cm-1

520408 -----14581416 --38603500

542 618 726 964 1031 1328 --

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1520 1631 34253749

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S0 cm-1

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557

CoPc cm-1 [17] --

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Samples

For S2 nanocomposite, the FTIR spectrum shows bands at 967, 1047, 1394 and 1530 cm-1 corresponding to the metal-ligand vibration, C–H in-plane deformation, C–C

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stretching and C–N stretching vibrations, respectively of iron phthalocyanine [18]. Bands positioned at 1650 cm-1 for S2 and 1631 cm-1 for S1 indicate the formation of Ti-OH bands in the

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nanocomposites [19, 20]. However, this mode is almost absent in S0 sample. Vibrations of chemisorbed water in the range of 3425-3860 cm-1 have been observed in all the spectra with a slight shift in their positions. Thus, all the peaks observed in S1 and S2 show considerable shift in their positions, which might be due to the particle size variation and chemical action formed between the interface of Co/FePc and TiO2 in the nanocomposites [22].

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3.2.5 Raman spectra Co/FePc is a planar molecule consisting of 57 atoms together and it exhibits D4h point

representation (by considering only internal vibrations) as:

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group symmetry [23-25]. The vibrations of this molecule can be classified into an irreducible

Ґvib= 14 A1g+ 13 A2g+ 14 B1g+ 14 B2g+ 13 Eg+ 6 A1u+ 8 A2u+ 7 B1u+ 7 B2u+ 28 Eu ,

where A1g, B1g, B2g, and Eg modes are found to be Raman-active while, the A1g, B1g, and B2g

vibrations as explained by Basova and Kolesov [24-26].

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(non-degenerate) modes are in-plane vibrations, and doubly degenerate Eg are the out-of-plane

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Raman spectra of the synthesized samples were recorded in the range of 50-1800 cm-1 as shown in Fig. 8. Table 3 compares the observed Raman modes in S0, S1 and S2 with literature

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values.

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Fig. 8 Raman spectra of samples S0, S1 and S2

From Fig.8, it is observed that Raman spectra of the composite samples S1 and S2 are

modified, when compared to sample S0. There are six Raman active modes for TiO2 at 147, 198, 400, 514, 519 and 641 cm-1. For S1 and S2 samples, these modes show considerable shifts (table 3) due to the variation in particle size. Some additional modes of vibrations are also observed in

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the composite spectra, attributed to the inter-molecular arrangement of phthalocyanines with TiO2 in the composites.

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Literature values CoPc [25] FePc [26] S2 145.4 --203 -----495 -----646 --598 -595 658 848 681 1478 1451 1491 1525 1541 1536 -567 --

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S0 147 198 400 514 519 641 ------

Sample S1 149.05 199 404 504 -641 676 847 1471 1541 568

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Table 3. Comparison of Raman modes of S0, S1 and S2

The sample S1 shows Raman modes at 568 cm-1 (A1g), 676 cm-1 (B1g), 847 cm-1 (A1g),

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1471 cm-1 (B2g) and 1541 cm-1 (B1g), which correspond to cobalt phthalocyanine. In sample S2, the peaks at 598 cm-1 (A1g), 658 cm-1 (B1g), 1478 cm-1(B2g) and 1525 cm-1 (B1g) stand for Raman

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modes of iron phthalocyanine. The low wavenumber Raman modes of phthalocyanines (from 568 to 847 cm-1 for the two composites) represent the vibrations of C-C bonds, and the B2g bands

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at higher wavenumber region (1471 cm-1 for S1 and 1478 cm-1 for S2) indicate pyrrole stretching vibration. Apart from these, B1g bands at 1541 cm-1 for S1 and 1525 cm-1 for S2 are the characteristic vibrations of C–N–C bridge bonds, associated with the vibrations of central atom of phthalocyanine molecule (Co/Fe) connected with nitrogen atoms [26].

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3.3 Optical properties 3.3.1 UV-Vis studies

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Fig. 9 presents the UV–Vis spectra of S0, S1 and S2. The spectra display the existence of absorption bands of metal phthalocyanine species on the surface of TiO2 in S1 and S2 nanocomposites. Comparing with pure TiO2, the optical absorption is high for composite samples in UV and visible regime, which make them suitable candidates for photovoltaic

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applications.

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Fig. 9 UV– Vis absorbance spectra of S0, S1 and S2

From Fig. 9, it is observed that the absorption edges of composite samples show a

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bathochromic shift with an increased absorption intensity revealing the perturbance in the electronic states of TiO2/MPc nanostructures [27]. B band (Sorret band) and Q bands of composite samples are found to be in the range of 320-750 nm. The absorption edge observed for S0 at 415 nm is shifted to 438 and 444 nm for the synthesized nanocomposites S1 and S2, respectively. For S1, the band from 570 to 700 nm is the characteristic Q-band absorption of CoPc, which arises due to π→π* excited electron transition from highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO)) transitions [28, 29]. First

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excitonic level Q1 is at 2.01 eV, while Q2 is observed at 1.82 eV with an energy difference of 0.19 eV between them. Moreover, it is observed that intensity of peak Q1 is higher than that of Q2, which shows CoPc exists in α-phase in the synthesized TiO2/CoPc nanocomposite.

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In the case of S2, the excitonic bands are extended in the region 620 to 750 nm with Q1 and Q2 at 1.84 and 1.7 eV, respectively which arise due to the π-π* electronic transitions [28, 29]. It is interesting that the bands appear in both composites are in visible and near infra-red

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regime, which is likely to enhance their photocatalytic performance.

Fig. 10 (αhν)2 versus hν graph of S0, S1 and S2

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The fundamental band gap Eg of samples can be calculated by plotting (αhν) 2 against hν

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values. Fig. 10 depicts the graph of (αhν) 2 versus hν. The optical band gaps of the samples are found to be 3.02, 2.88 and 2.69 eV for S0, S1 and S2, respectively. Lowering of band gap values for the composite samples confirm that inclusion of MPcs in TiO2 enhances the optical properties. This can find applications in the field of electro-photographic systems, diodes, laser printers, photovoltaic cells and photo-electrochemical devices [30-33].

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3.3.2 PL studies Fig. 11 shows the PL spectra of S0, S1 and S2 samples. Spectra of S1 and S2 are found to be modified as compared to pure TiO2, which may be due to the composite formation. The

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emission is found to be in visible regime for all the samples. Broad emission in the spectral range from 350 to 550 nm is observed for S0. The band edge free excitons and binding excitons result

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peaks at 405 and 485 nm, respectively [34, 35].

Fig. 11 PL spectra of pure TiO2 and TiO2/ MPc composites

By analyzing composite samples, it is found that some of the peaks are disappeared and

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some new peaks are formed in blue-green region, when comparing with S0. S1 exhibits a

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broader peak centered at 468 nm. While for S2, main peak is at 470 nm with additional visible peaks at 483 and 494 nm. All these peaks assure the successful combination of TiO2/MPc nanocomposite. Besides, intensity of S1 is higher than that of S0 and S2, which is due to the presence of metallic cobalt ions. The incorporation of different metal ions substantially affects the intensity and width of PL spectra [36, 37]. Fig.12 displays the chromaticity diagram of the samples S0, S1 and S2. Unique blue emission is obtained for S0 sample. But, S1 produces greenish-blue light and S2 emits blue-

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green rays. This result is also consistent with photoluminescence spectra of the samples. The chromaticity co-ordinates of the samples are given in table 4. In short, the synthesized samples may find application in the field of LEDs, electrochromic displays and in photosensitizers [38-

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40].

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Fig. 12 CIE chromaticity diagram of S0, S1 and S2

Table 4. Chromaticity co-ordinates of S0, S1 and S2 x

y

S0

0.1408

0.1261

S1

0.1337

0.1857

S2

0.1314

0.2191

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Sample

3.4. Photocatalytic activity

Visible light photoactivity of the synthesized nanocomposites is demonstrated using

methylene blue (MB) and rhodamine blue (RB), which are common industrial dyes. The sample kept in dark showed almost zero decomposition (not presented in this paper). Fig. 13 illustrates

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the efficiency of degradation of S0, S1 and S2 for the two test dyes within 90 min of solar

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irradiation.

Fig. 13 Efficiency of dye degradation of the samples in 90 minutes From Fig. 13, it is evident that TiO2/FePc nanocomposite (S2) exhibit highest efficiency

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for the degradation of both MB and RB in visible light, compared to S0 and S1. It is attributed to the enhanced structural and optical properties of nanocomposite structure. An efficiency of 97%

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was obtained for MB degradation and 88% for RB degradation by sample S2, which is the highest value ever reported without using any assisting material. Guo et al. have reported a degradation efficiency of 94% for methyl orange dye using modified FePc/TiO2 heterostructures assisted with H2O2 for 3h [41]. Samples S0 and S1 showed 81% and 91%, respectively for MB degradation and 73% and 78%, respectively for RB degradation after irradiating with visible

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light for 90 min. These results are also important in terms of photocatalytic degradation of dyes, as this is achieved without adding any assisting material for photocatalysis. Effect of different catalysts for the degradation of MB is given in Fig. 14 (a). The sample

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(S2) kept in dark condition showed almost zero decomposition. The figure obviously demonstrates that all the samples (S0, S1 and S2) exhibit very good visible light activity. Among the samples, the photocatalytic degradation is high for TiO2/FePc nanocomposite (S2). Fig. 14

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(b) depicts the photocatalytic degradation of TiO2/FePc nanocomposite (S2) for methylene blue in specific time intervals. Almost 100% of organic pollutants are decomposed within 90 minutes

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of visible light irradiation. In short, TiO2/FePc nanocomposite can be used as a potential

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candidate for eliminating the organic pollutants from waste water.

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Fig. 14 (a) Effect of different catalysts for the degradation of MB; (b) Photocatalytic degradation of MB using TiO2/FePc nanocomposite (S2)

The

mechanism

of

photocatalytic

activity

exhibited

by

TiO2/Phthalocyanine nanocomposites can be expressed as follows [41]. hν + M-Pc M-Pc* + O2 M-Pc* + TiO2

M-Pc*

(1) 1

M-Pc + O2

.

M-Pc * + TiO2 (e-)

(2) (3)

the

synthesized

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TiO2 (e-) + (O2 or 1O2)

.-

.

+ H2O

.-

(4)

-

HO2 + OH

.

(5)

.

HO2 + H2O

H2O2 + OH

(6)

.

H2O2

2OH

(7)

.

OH + (MB/RB)

CO2 + H2O

.

M-Pc * + (MB/RB)

M-Pc + (MB/RB)

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O2

TiO2 + O2

(8)

.+

(9)

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Extremely high visible light photocatalytic activity of TiO2/M-Pc nanocomposites compared to pure TiO2 nanoparticles are explained further. Sol-gel synthesized pure TiO2

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nanoparticles have band gap energy of 3.02 eV showing the limited range of photocatalytic process. As the optical band gap of the synthesized nanocomposites (2.88 eV for S1 and 2.69 eV for S2) extends into the visible region, chance of visible light driven photocatalytic property is higher. Eq. 1 to 9 form an account for the possible mechanism for the photocatalytic degradation

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of MB or RB using TiO2/M-Pc (M=Co, Fe) nanocomposites. Visible light irradiation on the nanocomposites produces exciting phthalocyanine (M-Pc) particles, which then follows a twostep (Eq. 2 and 3) charge transfer reaction. After a series of reactions (Eq.5 to 9) super oxide

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radical anions, hydroperoxy radicals and hydroxyl radicals are produced, which are powerful oxidizing and reducing agents. These can degrade harmful MB/RB dye molecules into CO2 and

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water. Also, the phthalocyanine dye radicals (M-Pc.*) can eliminate organic pollutants, thus by regaining parent phthalocyanine. A pictorial representation for the proposed mechanism of visible light active photocatalytic degradation of TiO2/M-Pc (M= Co, Fe) nanocomposites is given in Fig.15.

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Fig. 15 Schematic representation for the mechanism of visible light active photocatalytic

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degradation of TiO2/M-Pc (M= Co, Fe) nanocomposites 4 Conclusions

Using solvent-evaporation method, TiO2/M-Pc nanocomposites were synthesized successfully at low temperature. The thermal, structural, optical and photocatalytic properties of the synthesized samples were investigated. Growth of rutile phase (64.6%) was observed for

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TiO2/CoPc nanocomposite without calcination treatment. FTIR and Raman spectroscopic studies confirmed the successful formation of TiO2/M-Pc (M=Co/Fe) nanocomposites. Band gap tuning from UV to visible range for the TiO2/M-Pc nanocomposites was confirmed by UV-Vis

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spectroscopy, suggesting the possible applications in the field of electro-photographic systems,

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diodes, laser printers, photovoltaic cells, photo-electrochemical devices and in the field of photocatalytic dye degradation. The blue-green emission obtained for the samples may find potential in the near UV light excited LEDs. The photocatalytic degradation studies found that almost 100% of organic pollutants are decomposed within 90 minutes of visible light irradiation confirming the potential use of TiO2/M-Pc nanocomposites in the field of industrial applications to eliminate the organic pollutants from waste water. Acknowledgments

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The authors acknowledge their thanks to Nirmala College, Muvattupuzha, and Mangalore University, Mangalagangotri for providing the opportunity to undertake this study. They are also

References

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thankful to SAIF, Cochin for providing facilities for characterization.

1. A. A. Ansari, M. A. M. Khan, M.N. Khan, S.A. Alrokayan, M. Alhoshan, M. S. Alsalhi, J. Semicond. 32, 4 (2011) 043001–043006.

SC

2. N. Kobayashi, Bull. Chem. Soc. Jpn., 75 (2002) 1–19.

3. N. Ishida, D. Fujita; J. Phys. Chem. C. 116 (2012), 20300−20305.

M AN U

4. V. Iliev; J. Photochem. and Photobiol A: Chem. 151 (2002) 195–199.

5. Z. Wang, W. Mao, H. Chen, F. Zhang, X. Fan, G. Qian; Catalysis Communications. 7 (2006) 518–522.

6. Z. Wang, H. Chen, P. Tang, W. Mao, F. Zhang, G. Qian, X. Fan; Colloids and Surfaces A: Physicochem. Eng. Aspects. 289 (2006) 207–211.

(2014) 484–494.

TE D

7. A. Ebrahimian, M.A. Zanjanchi, H. Noei, M. Arvand, Y. Wang; J. Environ. Chem. Eng. 2

8. S. Liu, Z. Zhao, Z. Wang; Photochem. Photobiol. Sci., 6 (2007) 695–700.

EP

9. Z. Zhao, J. Fan, S. Liu, Z. Wang; Chem. Eng. Journal. 151 (2009) 134–140. 10. K. T. Ranjit, I. Willner; J. Phys. Chem. B., 102 (1998), 102, 9397-9403.

AC C

11. G.D. Sharmaa, R. Kumara, M.S. Roy; Solar Energy Materials & Solar Cells. 90 (2006) 32–45.

12. K P Priyanka, P A Sheena, N Aloysius sabu, T George, K M, Balakrishna and T Varghese Indian J Phys. 88 657 (2014)

13. F. V. Burgos, et al., Fuel. 99 (2012) 106–117. 14. S. F. Pop, R. M. Ion, J. Optoelectronics Adv. Mater. 12 (2010) 1976 – 1980.

ACCEPTED MANUSCRIPT

15. R.A. Spurr, H. Myers, Analytical Chem. 29, 5 (1957) 760-762. 16. B.D. Cullity, Elements of X-Ray Diffraction, Addison-Wesley, MA, 1967. 17. D. Verma, R. Dash, K. S. Katti, D. L. Schulz, A. N. Caruso; Spectrochimica Acta Part A.

RI PT

70 (2008) 1180–1186.

18. R. Seoudi, G. S. El-Bahy J. Molecular Structure. 753 (2005) 119-126.

19. Y. Zhao, C. Li, X. Liu, F. Gu, H. Giang, W. Shao, L. Zhang, Y. He; Mater. Lett. 61

SC

(2007) 79–83.

20. A.N. Jose, J.T. Juan, D. Pablo, R.P. Javier, R. Diana, I.L. Marta, Appl. Catal. A Gen. 178

M AN U

(1999) 191–203.

21. B. Joseph, C. S. Menon, E. J. Chem. 5 (2008) 86–92.

22. Xiao-fen Fan, Jie-min Liu; Journal of the Air & Waste Management Association. 65:1 (2015), 50-58, DOI: 10.1080/10962247.2014.962647

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23. J. Sforzini, F. C. Bocquet, F. S. Tautz; arXiv:1609.06894v1 [cond-mat.mtrl-sci] (2016). 24. T. Basova, B. Kolesov; J Struct Chem. 41 (2000) 770. 25. B. A. Kolesov, T. V. Basova; Thin Solid Films. 304 (1997) 166–169.

EP

26. M. Szybowicz, J. Makowiecki; J Mater Sci. 47 (2012) 1522–1530. 27. V. Mani, R. Devasenathipathy, Shen-Ming Chen, Jiun-An Gu, Sheng-Tung Huang,

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Renewable Energy. 74 (2015) 867e874.

28. C. C. Leznoff, A. B. P. Lever, Eds., Phthalocyanines:Properties and Applications, vol. 1, VCH Publishers, New York, NY, USA, 1990.

29. C. C. Leznoff, A. B. P. Lever, Eds., Phthalocyanines: Properties and Applications, vol. 4, VCH Publishers, New York, NY, USA, 1996. 30. S. Grammatica, S, J. Mort, Appl. Physics Lett. 38 (1981),445.

ACCEPTED MANUSCRIPT

31. A. Kakuta, Y. Mori, S. Takano, M. Sawada, I. Shibuya, J. Imag, Technol. 7 (1985). 32. A. K. Ghosh, D. L. Morel, T. Feng, R. F. Shaw, C. A. Rowe, J. Appl. Phys. 45 (1974) 230. 33. R. O. Loutfy, L. F. Mclntyne, Energy Mater. 6 (1982) 467.

RI PT

34. W. Li, C. Ni, H. Lin, C. P. Huang, S. Ismat Shah J. Appl. Phys. 96 (2004) 6663. 35. A.I. Kingon, J.P. Maris, S.K. Steiffer, Nature (London) 406 (2000) 1032.

36. G. A. Kumar, J. Thomas, N. George, B. A. Kumhakrishnan, V. P. N. Nampoori, C. P. G.

SC

Vallabhan, Physics and Chemistry of Glasses. 41, 2 (2000) 89-93.

37. M. E. Sánchez, J. C. Alonso, J. N. Reider, Adv. in Materials Physics and Chemistry, 1

M AN U

(2011) 57-63.

38. A. Sreedevi, K. P. Priyanka, K. K. Babitha, O. P. Jaseentha, Thomas Varghese, Eur. Phys. J. Plus 131: 7 (2016), DOI 10.1140/epjp/i2016-16007-9.

39. K. K. Babitha, K. P. Priyanka, A. Sreedevi, Bincy Abraham, J. K. Thomas, T. Varghese, J.

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Mater Sci: Mater Electron 28 (2017)1115-1123.

40. K. K. Babitha, K. P. Priyanka, O.P Jaseentha, A. Sreedevi, T. Varghese, Int. J. Appl. Ceram. Technol. 13(2016) 670-677.

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41. Z. Guo, B. Chen, J. Mu, M. Zhang, P. Zhang, Z. Zhang, J. W, X. Zhang, Y. Sun, C. Shao,

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Y. Liu, J. Hazardous Materials, 219-220 (2012) 156-163.

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Highlights TiO2/M-Pc nanocomposites synthesized by solvent evaporation method

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First report showing ~100% efficiency for pollutant degradation using TiO2/M-Pc

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First report showing formation of rutile TiO2 without calcination

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Band gap tuning of TiO2/M-Pc from UV to visible range for potential applications

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